In addition to its normal physiological functions, estrogen directs events that lead to both the protection from and promotion of many pathological conditions. However, the molecular details linking the binding of the receptor to its target genes with the ultimate biological consequence often remain unclear. In an attempt to define signaling cascades triggered by estrogen, the novel observation was made that the ZEB/dEF1 gene is induced at the transcriptional level by estrogen. Other data show that ZEB/dEF1 is one of the links in estrogen signal transduction pathways in reproductive tissues. For example, ZEB/dEF1 expression is high in rapidly proliferating endometrial and ovarian cancers but is no longer regulated by estrogen. In contrast, the gene is deleted in slowly growing endometrial cancers. These data suggest that ZEB/deltaEF1 plays a pivotal role in reproductive tissues. ZEB/deltaEF1 is a transcription factor that contains several functional domains including two zinc finger clusters at each terminus. Most data suggest that ZEB/deltaEF1 is a transcriptional repressor but in some circumstances it functions as a transcriptional activator. The overall goals of this proposal are to define the mechanism of gene activation by ZEB/deltaEF1 and to identify its target genes. The specific aims of this proposal are to 1). Investigate the mechanism of gene activation by ZEB/deltaEF1, 2). Identify the proteins in reproductive tissues that act as co-activators with ZEBdeltaEF1, and 3). Identify the downstream targets of ZEB/deltaEF1 in a breast cancer cell line. The first aim will be approached primarily by truncating ZEB/dEF1 and determining the effects on reporter gene activation. The second specific aim will be addressed by two complementary approaches, tandem mass spectrometry and a yeast two-hybrid Ras recruitment system. For the last specific aim, target genes for ZEB/deltaEF1 will be identified using gene profiling with DNA microarrays. These experiments will provide important information about the mechanism of gene activation by ZEB/deltaEF1 and about estrogen signal transduction pathways.